Fuel



Patented Feb. 18, 1936 uNrrru v STATES ea-Tear OFFICE Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.

, pression ignition fuels and it particularly relates to the use ofnovel ignition accelerators for the said fuels.

One'object of this invention relates to improvements in Diesel enginefuels, and particularly in fuels adapted for use in high-speedcompression ignition engines whereby to obtain reduction of the delayperiod between the injection and the ignitionof the fuel oil, areduction in the ignition temperature of the fuel oil and/or a loweringof the compression ratio of the engine. A more specific object relatesto compression ignition fuels containing as an ignition accelerator analkyl nitrate containing a branched carbon chain and corresponding tothe nitrates of the 1 higher alcohols produced by the catalytichydrogenation of carbon monoxide. Other objects of the invention willbecome apparent i'romthe following description.

In accordance with the present invention, it

- has been found thatwhen the nitrates of branched chain alcoholsobtainable by carbon monoxide hydrogenation are added to the fuel oilthere is obtained a reduction in the delay period between injection andignition of the fuel oil. This phenomenon is accomplished by a loweringof the ignition temperature of the-fuel oil and/or a lowering of thecompression ratio in the compression engine required to ignite the fuel.Alkyl nitrates of the character described have a substantial solubilityin fuel oil.

The following table illustrates the effect of the use of these alkylnitrates on the fuel oil characteristics. The properties of the dopedand modified fuel oil are compared with those of the unmodified fueloil:

sisted in injecting the fuel oil into air at atmospheric pressure into aheated. chamber. The ignition delay is the elapsed time betweeninjectionand ignition of the fuel. The minimum ignition temperature is the lowesttemperature at Application January 21, 1933, Serial No. 652,937

' comm. (01. 44-9) which a majority of a series of samples injected intothe chamber ignite. The minimum compression ratio was determinedaccording to the method described by Pope and Murdock in the Society ofAutomotive Engineers Journal, Transactions pages 136-142for March, 1932.

Tertiary butyl nitrate may be .used in lieu of isobutyl nitrate but thelatter is preferred due to the fact that isobutyl alcohol is availablein large quantities as a product of carbon monoxide hydrogenation.

In general, I have found that the nitrates of the branch chain alcoholsproduced by the hydrogenation of carbon monoxide are considerablysuperior to the ethyl and methyl nitrates which have hitherto beenproposed as Diesel fuel accelerators in that they are less volatile andconsequently reducethe hazards involved.

In addition to the branch chain butyl nitrates which can be used inaccordance with the present invention, other useful compounds comprisethe nitrates of alcohols other than isobutyl and likewise obtainable bythe catalytic hydrogenation of carbon monoxide. Those nitrates ofbranched chain alcohols having at least six carbon atoms areparticularly suitable since the use of these compounds in fuel oilsinvolves substantially no hazard because of the fact that they have verylow vapor pressures'and also because of the fact that they arecompletely miscible in the oil and W consequently can be stored andtransported in concentrated solutions in the 011 without danger ofhaving them separate out during cold weather. In accordance with thepresent invention, I may use either the secondary or the primaryalcohols or a mixture of these alcohols as formed in the hydrogenationof carbon monoxide.

The following illustrates one mode of preparing a nitrated productcapable of use in accordance with the present invention:

Example A fraction of alcohols obtained by the hydrogenation of carbonmonoxide and boiling above C. was nitrated by using a mixed acidcontaining 49.3% nitric acid and 51.44% sulfuric acid. The temperaturewas maintained at 8-l0 C. The alcohol was added cautiously to thenitrating mixture and when the reaction mixture began to fume off it wasdrowned in water and given the usual water and soda washes. The productwas thus obtained as a dark greenish oil.

I prefer however to separate the primary alcohols and nitrate themseparately inasmuch as the nitration of the individualprlmary alcoholson proceeds more smoothly. As specific examples of the primary branchedchain'alcohols other than isobutyl which are eminently suited fortheprep aration of nitrate accelerators, the following are mentioned:Z-methyl-l-pentanol, 2, 4-dimethyll-pentanol, 4-methyl-1-hexanol, 2,d-dimethyl one per cent up to the limit of solubility in the fuel,

but the preferred amount of accelerator ranges from one to five per centof the fuel.

The branched chain aliphatic nitrates comin within the scope of thepresent invention in-- clude those having four or more carbon atoms, butpreferably containing at least six carbons, the hydrocarbon contentconferring on the compoundsa high boiling point which increasesgenerally with increased carbon content.

The advantages of the use of these accelerators in fuel oil forcompression ignition engines are:

l. Elimination of knocking and rough-running by decreasing the ignitionlag.

2. Reduction of engine wear by removing the cause of knocking androughness.

3. Easier starting. The reduced spontaneous ignition temperatures of thedoped oil enables it to ignite much more easily when starting from cold.

4. Improved exhaust. Owing to the more complete combustion the exhaustis cleaner especially at higher speeds. No harmful constituents areintroduced into the exhaust gases by the combustion of the dope.

5. Possibility of use of inferior fuels. By the addition of dope, lowgrade fuels, at present quite unsuitable for compression ignitionengines, can be rendered equal or superior to high grade undoped fuels.

6. Naturev of dope. The dope has a neutral reaction, is non-toxic andsoluble in the oil.

'7. Improvements in engine design. Reduced engine stresses,resultingfrom the more gradually applied piston pressures, should makefor lighter scantlings while the more readily ignited and rapidlyburning fuel should render' possible the construction of smaller andfaster running engines.

8. Increased power and reduced fuel consumption. The improved combustionresulting from the explosive action of the dope enables a greaterproportion of the air charge to be burnt, and

further, as ignition takes place at once, the fuel .can be injectedduring the compression stroke at a smaller crank angle near top deadcenter.

The specific utility of the present invention results from the higherboiling points and lower vapor pressures of the branched ,chain alkylnitrates as compared with the ni described in the prior art. The boilingpoint of isobutyl primary nitrate (isopropyl methyl nitrate) is comparedwith the boiling points of straight chain lower alkyl nitrates:

Boiling Dope point C Methyl "mu. Ethyl nitrat 87 Propy trots 110.6Isobutyl primary nitrate 125 Further advantages are: l. The increasedboiling point prevents the formation of vapor locks in the fuel systemof the engine.

dopes also decreases the physiological effects,

such as headaches, which constitute an objection to lower alkylnitrates.

The above description and examples are to be taken as illustrative onlyand not as limiting the scope of. the invention. Any modification orvariation therefrom which conforms to the spirit of the invention isintended to be included within the scope of the claims.

I claim:

1. A compression ignition fuel comprising a fuel oil boiling above thegasoline range containing the nitrates of the mixture of open branchedchainaliphatic monohydric alcohols obtainable by the catalytichydrogenation of carbon monoxide and having at least four carbon atomsand containing isobutyl alcohol.

2. A compression ignition fuel comprising a fuel oil boiling above thegasoline range containing isobutyl nitrate obtainable by the nitrationof isobutyl alcohol, said alcohol being obtainable by the catalytichydrogenation of carbon monoxide.

CARL S. MARVEL.

